Monday, May 31, 2010

Astrophysicists at UC Santa Barbara are the first scientists to identify two white dwarf stars in an eclipsing binary system, allowing for the first direct radius measurement of a rare white dwarf composed of pure helium. The results will be published in the Astrophysical Journal Letters. These observations are the first to confirm a theory about a certain type of white dwarf star.

The story began with observations by Justin Steinfadt, a UCSB physics graduate student who has been monitoring white dwarf stars as part of his Ph.D. thesis with Lars Bildsten, a professor and permanent member of UCSB's Kavli Institute for Theoretical Physics, and Steve Howell, an astronomer at the National Optical Astronomy Observatory (NOAO) in Tucson, Ariz.

Brief eclipses were discovered during observations of the star NLTT 11748 with the Faulkes Telescope North of the Las Cumbres Observatory Global Telescope (LCOGT), a UCSB-affiliated institution. NLTT 11748 is one of the few very low-mass, helium-core white dwarfs that are under careful study for their brightness variations. Rapid snapshots of the star –– about one exposure every minute –– found a few consecutive images where the star was slightly fainter. Steinfadt quickly realized the importance of this unexpected discovery. "We've been looking at a lot of stars, but I still think we got lucky!" he said.

Avi Shporer, a postdoctoral fellow at UCSB and LCOGT, assisted with the observations and quickly brought his expertise to the new discovery. "We knew something was unusual, especially as we confirmed these dips the next night," Shporer said. The scientists observed three-minute eclipses of the binary stars twice during the 5.6-hour orbit.

The excitement of the discovery and the need to confirm it rapidly led to the use of the 10-meter Keck Telescope, located on Mauna Kea in Hawaii, just five weeks after the first observation. The team also brought in David Kaplan, a Hubble Fellow and KITP postdoctoral fellow. Bildsten and Kaplan arranged for use of the Keck by swapping time they had reserved for another project with Geoff Marcy at UC Berkeley.

During that night, the scientists were able to measure the changing Doppler shift of the star NLTT 11748 as it orbited its faint, but more massive, white dwarf companion. "It was amazing to witness the velocity of this star change in just a few minutes," said Kaplan, who was present at the Keck telescope during the observations.

These observations led to the confirmation of an important theory about white dwarf stars. Stars end their lives in many ways. "The formation of such a binary system containing an extremely low mass helium white dwarf has to be the result of interactions and mass loss between the two original stars," said Howell. White dwarf stars are the very dense remnants of stars like the sun, with dimensions comparable to the earth. A star becomes a white dwarf when it has exhausted its nuclear fuel and all that remains is the dense inner core, typically made of carbon and oxygen.

One of the stars in the newly discovered binary is a relatively rare helium-core white dwarf with a mass only 10 to 20 percent of that of the sun. The existence of these special stars has been known for more than 20 years. Theoretical work predicted that these stars burn hotter and are larger than ordinary white dwarfs. Until now, their size had never been measured. The observations of the star NLTT 11748 by this research group have yielded the first direct radius measurement of an unusual white dwarf that confirms this theory.

The other star in the binary is also a white dwarf, albeit a more ordinary one, composed of mostly carbon and oxygen with about 70 percent of the mass of the sun. This star is more massive and also much smaller than the other white dwarf. The light it gives off is 30 times fainter than that of its partner star in the binary.

Bildsten credits the scientific collaborations at UCSB for the success of this work, noting that the original team was expanded to include KITP, the Physics Department, and LCOGT to quickly respond to the new discovery.

"A particularly intriguing possibility to ponder is what will happen in 6 to 10 billion years," said Bildsten. "This binary is emitting gravitational waves at a rate that will force the two white dwarfs to make contact. What happens then is anybody's guess."

Sleeping newborns are better learners than thought, says a University of Florida researcher about a study that is the first of its type. The study could lead to identifying those at risk for developmental disorders such as autism and dyslexia.

“We found a basic form of learning in sleeping newborns, a type of learning that may not be seen in sleeping adults,” said Dana Byrd, a research affiliate in psychology at UF who collaborated with a team of scientists.

The findings give valuable information about how it is that newborns are able to learn so quickly from the world, when they sleep for 16 to 18 hours a day, Byrd said. “Sleeping newborns are better learners, better ‘data sponges’ than we knew,” she said.

In order to understand how newborns learn while in their most frequent state, Byrd and her colleagues tested the learning abilities of sleeping newborns by repeating tones that were followed by a gentle puff of air to the eyelids. After about 20 minutes, 24 of the 26 babies squeezed their eyelids together when the tone was sounded without the puff of air.

“This methodology opens up research areas into potentially detecting high risk populations, those who show abnormalities in the neural systems underlying this form of learning,” she said. “These would include siblings of individuals with autism and siblings of those with dyslexia.”

The research team’s paper, published online this week in Proceedings of the National Academy of Sciences, describes the results of their experiment with the 1- or 2-day-old infants, comparing them with a control group using EEG and video recordings. The brain waves of the 24 infants were found to change, providing a neural measurement of memory updating.

“While past studies find this type of learning can occur in infants who are awake, this is the first study to document it in their most frequent state, while they are asleep,” Byrd said. “Since newborns sleep so much of the time, it is important that they not only take in information but use the information in such a way to respond appropriately.”

Not only did the newborns show they can learn to give this reflex in response to the simple tone, but they gave the response at the right time, she said.

Learned eyelid movement reflects the normal functioning of the circuitry in the cerebellum, a neural structure at the base of the brain. This study’s method potentially offers a unique non-invasive tool for early identification of infants with atypical cerebellar structure, who are potentially at risk for a range of developmental disorders, including autism and dyslexia, she said.

The capacity of infants to learn during sleep contrasts with some researchers’ stance that learning new material does not take place in sleeping adults, Byrd said.

The immature nature of sleep patterns in infants could help explain why, she said.

“Newborn infants’ sleep patterns are quite different than those of older children or adults in that they show more active sleep where heart and breathing rates are very changeable,” she said. “It may be this sleep state is more amenable to experiencing the world in a way that facilitates learning.”

Another factor is that infants’ brains have greater neural plasticity, which is the ability for the neural connections to be changed, Byrd said. “Newborns may be very adaptive to learning in general simply because their brains have increased plasticity, increased propensity to be changed by experience,” she said.

The ancestor of all hammerhead sharks probably appeared abruptly in Earth's oceans about 20 million years ago and was as big as some contemporary hammerheads, according to a new study led by the University of Colorado at Boulder.

But once the hammerhead evolved, it underwent divergent evolution in different directions, with some species becoming larger, some smaller, and the distinctive hammer-like head of the fish changing in size and shape, said CU-Boulder Professor Andrew Martin of the ecology and evolutionary biology department.

Sporting wide, flattened heads known as cephalofoils with eyeballs bulging at each end, hammerhead sharks are among the most recognizable fish in the world. The bizarre creatures range in length from about 3 feet up to 18 feet and cruise warm waters around the world, Martin said.

In the new study, scientists focused on the DNA of eight species of hammerhead sharks to build family "gene trees" going back thousands to millions of generations. In addition to showing that small hammerheads evolved from a large ancestor, the team showed that the "signature" cephalofoils of hammerheads underwent divergent evolution in different lineages over time, likely due to selective environmental pressures, said Martin.

The team used both mitochondrial DNA passed from mother to offspring and nuclear DNA -- which is commonly used in forensic identification -- to track gene mutations. The researchers targeted four mitochondrial genes and three nuclear genes, which they amplified and sequenced for the study.

A paper on the subject was published in this month's issue of Molecular Phylogenetics and Evolution. Led by former CU-Boulder ecology and evolutionary biology undergraduate student Douglas Lim, co-authors included Martin and University of South Florida researchers Philip Motta and Kyle Mara. Lim is currently a student at the University of Colorado School of Medicine. The National Science Foundation funded the study.

The researchers sampled hammerheads from across the globe -- including the waters of the southeast United States now under siege by the Gulf oil spill -- as well as Australia, Panama, Hawaii, Trinidad and South Africa. Most of the hammerhead DNA was obtained at local markets, where the peddling of sharks and other fish is common practice.

The team sequenced the DNA of the sharks, constructing a "phylogenetic" tree that shows how all of the species are related and when each species originated, said Martin. The hammerhead ancestor probably lived in the Miocene epoch about 20 million years ago.

The team found that two divergent lineages of small sharks about 3 to 4 feet long originated independently at separate times in the past. One of the species, the winghead shark, now lives in the warm waters north of Australia and the other, the bonnethead shark, inhabits the Caribbean and tropical eastern Pacific Ocean.

One reason for the "incredible shrinking shark" over the eons may be the process of neoteny -- the ability of some adult sharks to retain juvenile traits -- or their ability to achieve sexual maturity at earlier ages, Martin said. "As the sharks became smaller, they may have begun investing more energy into reproductive activities instead of growth."

While the cephalofoils appear to provide "lift" to large hammerheads as they cruise through the water -- much like the wing of an airplane -- smaller hammerheads don't appear to gain an advantage in lift, but may gain other attributes. "It looks like they sacrifice locomotion advantages for prey detection and visualization," he said.

Another advantage hammerheads may gain from larger cephalofoils is an increased number of electrical sensors in their flattened noses and heads that can detect extremely weak electrical emissions from molecules associated with potential prey. "Hammerheads appear to be able to triangulate on their prey, which is remarkable," said Martin.

Small sharks are highly variable in the size and shape of their cephalofoils, said Martin. The winghead shark, for example, has a laterally expanded head that is about half the size of its roughly 4-foot body length. At the other end of the spectrum is the bonnethead shark, about 3 feet long but which has the smallest cephalofoil of all hammerhead species -- a protrusion that resembles the head of a shovel, Martin said.

Martin said that hammerheads are an ideal biological study subject in part because of some important similarities to humans. Both have slow growth rates, mature late in life, give live birth and have relatively few offspring. While hammerheads may have a dozen or more pups, other oceanic fish regularly lay millions of eggs. Hammerheads generally live for about 30 years, he said.

While hammerhead sharks appear intimidating, attacks on humans are extremely rare, said Martin. Hammerheads have relatively small mouths facing downward that are used to grab food like fish, shellfish, shrimp, squid, octopuses and stingrays. "If you see a hammerhead, I'd say grab your camera and jump into the water," said Martin.

"Hammerheads are special fish, and there is nothing that remotely resembles them anywhere on the planet," said Martin. Unfortunately, hammerheads -- like most shark species -- are on the decline. In addition to being overfished, sharks often are the victims of a technique known as finning, in which fishermen catch them, cut off their fins for use in delicacy soups, and return them to the water to die, Martin said. Shark meat also is used for fertilizer and to make pet food.

There currently are 233 shark species on the International Union for the Conservation of Nature's "Red List of Threatened Species," and 12 shark species are classified as critically endangered. A study led by Virginia Tech showed the great hammerhead, scalloped hammerhead and smooth hammerhead species declined by an average of 90 percent from 1981 to 2005. "Their situation is generally pretty dire," Martin said.

A 2005 study by Martin and his colleagues on scalloped hammerheads indicated females tend to breed in the specific ocean regions where they were born, while males tended to move around more widely. A previous study by Martin's team also showed that male great white sharks roam Earth's oceans much more widely than females, a finding with implications for future conservation strategies for the storied and threatened fish.

A mass extinction of fish 360 million years ago hit the reset button on Earth's life, setting the stage for modern vertebrate biodiversity. The mass extinction scrambled the species pool near the time at which the first vertebrates crawled from water towards land.

Those few species that survived the bottleneck were the evolutionary starting point for all vertebrates--including humans--that exist today, according to results of a study published in the journal Proceedings of the National Academy of Sciences (PNAS).

"Everything was hit; the extinction was global," said Lauren Sallan of the University of Chicago and lead author of the paper. "It reset vertebrate diversity in every single environment, both freshwater and marine, and created a completely different world."

The Devonian Period, which spanned from 416 to 359 million years ago, is also known as the Age of Fishes for the broad array of species present in Earth's aquatic environments.

Armored placoderms such as the gigantic Dunkleosteus and lobe-finned fishes--similar to the modern lungfish--dominated the waters, while ray-finned fishes, sharks and tetrapods were in the minority, according to Maureen Kearney, program director in the National Science Foundation (NSF)'s Division of Environmental Biology, which funded the research, along with NSF's Division of Earth Sciences.

But between the latest Devonian Period and the subsequent Carboniferous period, placoderms disappeared and ray-finned fishes rapidly replaced lobe-finned fishes as the dominant group, a demographic shift that persists to today.

"The Devonian period is known as the Age of Fishes, but it's the wrong kind of fish," Sallan said. "Just about everything dominant in the Devonian died at the end of the period and was replaced."

"There's some sort of pinch at the end of the Devonian," said the paper's second author, Michael Coates, an organismal biologist and anatomist at the University of Chicago.

"It's as if the roles persist, but the players change: the cast is transformed dramatically. Something happened that almost wiped the slate clean, and, of the few stragglers that made it through, a handful then re-radiate spectacularly."

Scientists have long theorized that the Late Devonian Kellwasser event--considered to be one of the "Big Five" extinctions in Earth's history--was responsible for a marine invertebrate species shake-up.

But an analysis of the vertebrate fossil record by Sallan and Coates pinpointed a critical shift in diversity to the Hangenberg extinction event 15 million years later.

Prior to the extinction, lobe-finned forms such as Tiktaalik and the earliest limbed tetrapods such as Ichthyostega had made the first tentative "steps" toward a land-dwelling existence.

But after the extinction, a long stretch of the fossil record known as "Romer's Gap," is almost barren of tetrapods, a puzzle that had confused paleontologists for many years.

Sallan and Coates' data suggest that the 15-million-year gap was the hangover after the traumatic Hangenberg event.

"Something that's seen after an extinction event is a gap in the records of survivors," Sallan said. "You have a very low diversity fauna, because most things have been killed off."

When tetrapods finally recovered, those survivors were likely the great-great-grandfathers to the vast majority of land vertebrates present today.

Modern vertebrate traits--such as the motif of five-digit limbs that is shared by all mammals, birds and reptiles in utero--may have been set by this early common ancestor, the authors propose.

"Extinction events remove a huge amount of biodiversity," Coates said. "That shapes in a very significant way the patchiness of biodiversity that persists to the present day."

The analysis benefitted from recent advances in filling in the vertebrate fossil record, Coates said.

Previously, estimates of the earlier extinction had been made using fossils of invertebrates such as mollusks and clams, which are far more abundant.

With a larger dataset of vertebrates and analytical techniques borrowed from modern ecology, Sallan and Coates were able to see the abrupt changes in species composition before and after the Hangenberg event.

"It's a big extinction during what was already considered a critical time in vertebrate evolution, so it's surprising that it went unnoticed for so long," Sallan said. "But it took the right methods to reveal its magnitude."

What remains mysterious is exactly what happened 360 million years ago to trigger this mass extinction.

Other researchers have found evidence of substantial glacier formation at the end of the Devonian period, which would have dramatically lowered sea levels and affected life.

The first appearance of forest-like environments in some regions might also have produced atmospheric changes catastrophic to animal life.

The research also raises questions about the pattern of evolution after the extinction event.

It remains unclear why groups that were abundant before the event did not recover, while other groups spread and diversified in radical new ways.

Regardless of these questions, the consequences are still being felt hundreds of millions of years later.

"It is a pivotal episode that shaped modern vertebrate biodiversity," Coates said. "We are only now beginning to place that important event in the history of life and the history of the planet, which we weren't able to do before."

So close and yet so wrong – you might love heavy metal like Metallica but your music platform suggests you should also like the Sixties sound of The Doors, simply because both bands are classified as rock.

New research published in New Journal of Physics (co-owned by the Institute of Physics and German Physical Society), shows that searching for the temporal aspects of songs – their rhythm – might be better to find music you like than using current automatic genre classifications.

By studying similar and different characteristics of specific rhythmic durations and the occurrence of rhythmic sequences, the group of Brazilian researchers has found that it is possible to correctly identify the musical genres of specific musical pieces.

The researchers studied four musical genres – rock, blues, bossa nova and reggae – looking at 100 songs from each category, analysing the most representative sequences of each genre-specific rhythm such as the 12 bar theme in blues, which means that the song is divided into 12 bars – or measures - with a given chord sequence.

Using hierarchical clustering, a visual representation of rhythmic frequencies, the researchers were able to discriminate between songs and come up with a possibly novel way of defining musical genres.

As the researchers write, "By showing that rhythm represents a surprisingly distinctive signature of some of the main musical genres, the work suggests that rhythm-based features could be more comprehensively incorporated as resources for searching in music platforms.

Musical genre classification is a nontrivial task even for musician experts, since often a song can be assigned to more than one single genre. With our proposed method, new sub-genres (for example, rock-blues) can arise from original ones. Therefore, we observed a significant improvement in the supervised classification performance."

The next step, as suggested by the researchers, would be to include further aspects such as the intensity of the beat in future research, which could increase accurate genre identification even more.

Greenland is situated in the Atlantic Ocean to the northeast of Canada. It has stunning fjords on its rocky coast formed by moving glaciers, and a dense icecap up to 2 km thick that covers much of the island--pressing down the land beneath and lowering its elevation. Now, scientists at the University of Miami say Greenland's ice is melting so

According to the study, some coastal areas are going up by nearly one inch per year and if current trends continue, that number could accelerate to as much as two inches per year by 2025, explains Tim Dixon, professor of geophysics at the University of Miami Rosenstiel School of Marine and Atmospheric Science (RSMAS) and principal investigator of the study.

"It's been known for several years that climate change is contributing to the melting of Greenland's ice sheet," Dixon says. "What's surprising, and a bit worrisome, is that the ice is melting so fast that we can actually see the land uplift in response," he says. "Even more surprising, the rise seems to be accelerating, implying that melting is accelerating."

Dixon and his collaborators share their findings in a new study titled "Accelerating uplift in the North Atlantic region as an indicator of ice loss," The paper is now available as an advanced online publication, by Nature Geoscience. The idea behind the study is that if Greenland is losing its ice cover, the resulting loss of weight causes the rocky surface beneath to rise. The same process is affecting the islands of Iceland and Svalbard, which also have ice caps, explains Shimon Wdowinski, research associate professor in the University of Miami RSMAS, and co-author of the study.

"During ice ages and in times of ice accumulation, the ice suppresses the land," Wdowinski says. "When the ice melts, the land rebounds upwards," he says. "Our study is consistent with a number of global warming indicators, confirming that ice melt and sea level rise are real and becoming significant."

Using specialized global positioning system (GPS) receivers stationed on the rocky shores of Greenland, the scientists looked at data from 1995 onward. The raw GPS data were analyzed for high accuracy position information, as well as the vertical velocity and acceleration of each GPS site.

The measurements are restricted to places where rock is exposed, limiting the study to coastal areas. However, previous data indicate that ice in Greenland's interior is in approximate balance: yearly losses from ice melting and flowing toward the coast are balanced by new snow accumulation, which gradually turns to ice. Most ice loss occurs at the warmer coast, by melting and iceberg calving and where the GPS data are most sensitive to changes. In western Greenland, the uplift seems to have started in the late 1990's.

Melting of Greenland's ice contributes to global sea level rise. If the acceleration of uplift and the implied acceleration of melting continue, Greenland could soon become the largest contributor to global sea level rise, explains Yan Jiang, Ph.D. candidate at the University of Miami RSMAS and co-author of the study.

"Greenland's ice melt is very important because it has a big impact on global sea level rise," Jiang says. "We hope that our work reaches the general public and that this information is considered by policy makers."

This work was supported by the National Science Foundation and NASA. The team plans to continue its studies, looking at additional GPS stations in sensitive coastal areas, where ice loss is believed to be highest.